Technical Field
The invention relates to control for a motor that drives a hydraulic pump in a hydraulic unit for a machining tool.
Related Art
In a hydraulic unit, a motor is coupled to a hydraulic pump, and the motor is rotated under feedback control based on a detection value from a hydraulic sensor and the like, whereby a hydraulic pressure is provided. Since such a hydraulic unit is provided with a hydraulic sensor and the like, various attempts are being made to detect abnormality of a hydraulic circuit based on detection values from the hydraulic sensor and the like.
FIG. 4 illustrates a block diagram of a motor control device that drives a hydraulic pump of a conventional technique. A hydraulic circuit includes a hydraulic pump 9 and selector switches 12a and 12b that switch the hydraulic circuit based on a switching command Ss from an upper-level control device 1 such as solenoids. The hydraulic circuit operates actuators 14a and 14b such as hydraulic cylinders. In the hydraulic circuit, a hydraulic pressure detection value Pd of a hydraulic sensor 10 provided between the hydraulic pump 9 and the selector switches 12a and 12b is fed back. Then, a deviation between a hydraulic pressure command value Pc output from the upper-level control device 1 and the hydraulic pressure detection value Pd is calculated as a hydraulic deviation by a subtractor 2. A speed command arithmetic unit 3 outputs a speed command value Vc through proportional-integral control based on the hydraulic deviation.
In order to rotate the hydraulic pump 9, a motor 8 is coupled to the hydraulic pump 9, and a motor position detector 7 is attached to the motor 8. A differentiator 15 differentiates a position detection value detected by the motor position detector 7 to output a speed detection value Vd of the motor. Then, a subtractor 4 calculates a deviation between the speed command value Vc and the speed detection value Vd of the motor and outputs the deviation as a speed deviation. Based on the speed deviation, a torque command arithmetic unit 5 outputs a torque command Tc through proportional-integral control. Based on the torque command Tc, a current controller 6 including an inverter causes current to flow to the motor to control the motor. In addition, a hydraulic pressure abnormality detector 17 detects that hydraulic pressure is abnormal based on hydraulic pressure detection values Pad and Pbd detected by the hydraulic sensors 13a and 13b provided between the selector switches 12a and 12b and the actuators 14a and 14b, and the switching command Ss, and reports the abnormality to the upper-level control device.
FIG. 5 illustrates a specific block diagram of the hydraulic pressure abnormality detector. The hydraulic pressure abnormality detector compares the hydraulic pressure detection values Pad and Pbd and a hydraulic pressure threshold for abnormality detection Aap or a hydraulic pressure threshold abnormality detection Abp that is selected by a selector 173 based on the switching command Ss and using a comparator 174. Based on the comparison result, a counter 175 detects a hydraulic pressure drop time. The hydraulic pressure drop time and is compared with a time threshold for abnormality detection Aat or a time threshold for abnormality detection Abt selected by a selector 178 based on the switching command Ss, by a comparator 179. When the actuator 14a is operated in a state where a leakage amount is large due to some abnormality of the actuator 14a, a time period until the hydraulic pressure detection value Pad drops becomes long. As a result, the hydraulic pressure drop time detected by the counter becomes long. When the hydraulic pressure drop time becomes longer than the time for abnormality detection Aat, the threshold comparator 179 detects abnormality, reports the abnormality to the upper-level control device, and reports to an operator that the hydraulic circuit or the actuator is abnormal.
The conventional technique illustrated in FIG. 4 has a problem that abnormality cannot be found upon failure of the hydraulic pump or occurrence of leakage from a passage from the pump to the selector switch in the hydraulic circuit. In addition, many hydraulic sensors are needed, causing an increase in cost, which can be a problem.